Arc attenuator



Sept. 3, 1963 c. F.'BRUNNER ARC ATTENUATOR Filed June 7, 1961 INVEN TOR.(AZL A; sea/wee AT 6 5y United States Patent 3,102,937 ARC ATTENUATORCarl F. Brunncr, Floral Park, N.Y., assignor to Murray 7 This inventionrelates to circuit breakers for opening and closing electric circuits,and more particularly this invention relates to improved are attenuatingmeans for electromagnetic type circuit breakers.

More specifically, this invention relates to a compact, molded case typeof electromagnetic circuit breaker such as described in Patent No.2,890,306 for Electromagnetic Circuit Breaker, issued June 9, 1959, toRypinski et al. and assigned to Murray Manufacturing Corporation. Thepatented circuit breaker comprises the usual handle for manually openingand closing the breaker circuit, electromagnetic means for actuating aspring-loaded trip mechanism, whereby in response to a predeterminedoverload condition the breaker is automatically tripped into the openposition, and a partially enclosed switch contact cavity within the casefor substantially confining the effects of arcing. The patented circuitbreaker also has a U-shaped magnetic member located to par"- tiallyenclose the path of a movable switch contact as it travels in the cavityfor are cutofi, when the breaker is opened under load. This inventionhas particular utilityin connection with the aforementioned. patentedcircuit breaker.

The patented circuit breaker is primarily designed for rated capacitiesof 20 amperes or less. At higher current ratings the single U-shaped arcsuppressor is inadequate to extinguish the arc sufficiently rapidly toprevent damage to the contacts and the casing in close proximity to thecontacts.

There are, of course, many known forms of arc suppressors for use incircuit breakers. However, the known forms could not be adapted for theaforesaid circuit breaker without requiring substantial modification tothe casing or to the general construction of the circuit breaker.

Standardization of electrical components has become extremely importantin the electrical industry because of the keenness of competition andthe desire to make relatively few components serve similar functions indifferent devices. 7

Accordingly, it is an object of the invention to provide a, novel areattenuating arrangement for use in the above mentioned circuit breaker,requiring no material change in the construction of the casing.

It is another object of the invention to provide a novel are attenuatingarrangement in the above mentioned type of circuit breaker which,because of its arc suppressing ability, permits the use of standardcomponents in breakers of different ratings within a given range,excluding, of course, current carrying components.

A further object of the invention is to provide such improved arcattenuation means without sacrifice to the existing advantages in theabove mentioned type of cir cuit breakers.

A still further object of my invention is to provide improved arcattenuation means entirely within the existing switch contact cavity ofthe circuit breaker.

According to an embodiment of my invention, I pro- Vide a secondmagnetic memberin cooperation with the above mentioned U-shaped arcsuppressor member which is so shaped and located as to cause the arc toextend in zig-zag fashion from one contact to the other. The zig- 'zagconfiguration effectively elongates the lengthy of the are and therebyshortens its duration for a given overload.

1" he shape and orientation of the second magnetic member cause an arcdeflection which directs the gases through the existing exhaust outletin the cavity. Specifically, the second magnetic member is in the formof an H and located so that the cross-bar of the H is opposed to thebase of the U-shaped arc suppressor, and the legs of the U and the upperarms of the H extend towards each other in overlapping, spacedrelationship.

The hot ionized gases are therefore more rapidly removed from the switchcontact cavity and the dielectric properties of air between the contactsare more rapidly restored. Thus, arc lifetime and consequent thermal andchemical damage to switch contacts and other components are minimizedand the higher amperage arc may be safely extinguished.

From the outside the circuit breaker incorporating the invention appearsidentical to the patented circuit breaker having a lower current rating.Increased current rating is obtained with only one added part. Neitherincreased size nor additional 'volume inside the case are required. Thesecond magnetic member of the invention is simple to fabricate and iseasily installed. All that is required for installation is incorporationof supporting ridges, grooves, or the like in the plastic case. No otherchanges in the circuit breaker are necessary for improved arc cutoifability, and the prior advantages of simplicity and compactness arepreserved.

The above mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood byreference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawing, wherein:

FIG. 1 is a front end viewof a circuit breaker incorporating anembodiment of my invention;

FIG. 2 is a side view of the circuit breaker of FIG. 1 with the coverremoved; and

FIG. 3 is a partial perspective view'of the switch cavity showing thecontacts and are suppressing arnangement.

As previously mentioned, an object of the invention is to utilize asmany components as possible from the patented breaker. Since thepatented breaker is disclosed in detailin the aforesaid patent, theseveral parts will not be described in detail herein. Only those partswill be described which are necessary for an understanding of theinvention.

Referring now to the figures, the circuit breaker comprises a moldedcase 1, including a cover 2, which supports and contains the severalparts.

An electrical contact clip 3 is provided at the front end of the breakerfor plug-in connection to a bus-bar (not shown).

A load connector-4 is provided at the rear end of the breaker forconnection to a circuit or a load wire. The electrical circuit of thebreaker comprises a coil 5, one end of which is connected to the springcontact clip 3, an electrically conductive spring member 6 connected tothe opposite end' of the coil 5, a movable contact 7 connected to an endof the conductive spring member 6, and a stationary contact 8 attachedto an extension 9 of the load connector 4.

The contacts 7 and 8 are closed when a handle 10 is moved to the right,in the sense of the drawing, about a shaft. 19A causing its cam surfaceI11 to depress a cam follower plate 12 about a pivot support 13. The camrfollower plate 12. is thus moved downwardly (continuing in the sense ofthe drawing). against an actuating plate 14- which bears against anddrives a roller assembly 1-5 in a guided slot 16. The lower end of theroller amass? assembly actuates the conductive spring member 6 in thedownward direction causing the movable contact 7 to come into engagementwith the stationary contact 8-.

As best seen in FIGS. 2 and 3, the two contacts are located in a cavitywithin the case. Movement of the contact 7 is entirely within thiscavity. Barrier walls 1'7, 18 on opposite sides of the cavity affordpartial closure thereof. The barriers serve to protect adjacent parts ofthe breaker from arcing defects. The upper part of barrier 17 alsoserves to limit movement of the spring conductor 6 when the movablecontact is displaced from the fixed contact. A passage or duct 19 isprovided from the fixed contact side of the cavity through the case 10for exhausting gases when an arc occurs in the cavity.

The electromagnetic circuitry comprises the coil which surrounds asealed tube 20 containing a movable pole piece in a damping medium suchas a silicone coil. At one end of the tubular member a fixed pole piece21 is provided. The movable pole piece within the tubular member isspring urged in the direction opposite the fixed pole piece. Excessivecurrent flowing through the coil 5 tends to urge the movable pole piecetowards the fixed pole piece. If excessive current is maintained for aperiod of time sufiicient for the movable pole piece to reach the fixedpole piece, the magnetic field is intensified to such an extent that anarmature member .23 is attracted to the fixed .pole piece 21. Thearmature is rockably mounted at 24 within the side walls of the casingso that the lower leg thereof, in being attracted to the fixed polepiece, will trip the plate member 14 off the roller assembly 15, therebyreleasing the spring member 6 to separate the movable contact from thefixed contact.

Referring now specifically'to the arc suppressing arrangement (FIG. 3),a U-shaped member 25 is located in the cavity where it is supported bygrooves in the barrier wall 17 and the case of the breaker. The U-shaped member '25 is formed of magnetic material and is positioned withits base portion against the wall 17. The legs 26, 27 of the U projectalong opposite sides of the path of the movable contact. As discussedpreviously, this single magnetic member is adequate for are cutoff inbreakers rated 20 amperes or less.

As is well known 'when an arc is drawn between two contacts such as 7and '8, numerous potentially destructive mechanisms are present. Thereis of course heating which may be suflicient to melt adjacentcomponents. The dielectric medium between the contacts (air in thepresent case) breaks down and becomes a good conductor. A gaseousdielectric is heated making increased pressure a potential hazard. Agaseous dielectric also becomes ionized and extremely reactive therebycausing sputtering which results in pitting or rapid corrosion at thecontact surfaces.

The total amount of damage which can be done by an arc depends on powerand time. The interrupting capacity of a circuit breaker is dependentuponthe amount of time required to extinguish an arc drawn betweencontacts when the breaker is opened. Accordingly, for arcs of highamperage steps must be taken to shorten arc lifetime in order tominimize risks of arc damage.

The second magnetic member serves magnetically to.

displace the are when it is drawn between the contacts upon opening ofthe movable contact. The are is displaced from a straight'line pathbetween the contacts to the cross-bar .29 as the movable contact 7passes the second magnetic member 28. As the contact continues in itsmovement, it passes between the legs 26, 27 and the arc is thendeflected to the base of the U. The path of the arc is shown by brokenline in FIG. 3 and as observed is substantially elongated from thestraight path it would have assumed in the absence of the secondmagnetic member 28.

Also, as shown, the cross-bar of the second magnetic member ispositioned on the side of the path adjacent to duct 19, and the spacebetween the legs 32, 33 of the H presents an unobstructed opening inalignment with the duct 19. Thus, the arc is displaced to the cross-barand also towards the exhaust outlet. This means that hot ionized gasesproduced by the arc in the vicinity of duct may be rapidly exhausted.With the second magnetic member of this invention, the totaltimerequired to exhaust hot, ionized gases from the cavity is minimal.This not only permits rapid cooling of the cavity but also permits rapidrehabilitation of the dielectric properties of the air between thecontacts.

While theforegoing description sets forth the principles of theinvention in connection with specific apparatus, it.

is to be understood that this description is made only by way of exampleand not as a limitation of the scope of the invention as set forth inthe objects thereof and in the accompanying claims.

I claim:

1. A circuit breaker comprising, in combination, a case having internalopposing barrier walls defining a partially enclosed cavity therein andhaving a passage communicating between said cavity and the outside ofthe case; switch means disposed in said case and including a fixedcontact mounted in said cavity and a movable contact located in saidcavity and capable of limited movement between opened and closedpositions; means mounted in said case and responsive to overloadconditions for opening said switch means; a U-shaped magnetic membersupported in said cavity adjacent the path of movement of said movablecontact with the side arms thereof embracing said path and the basethereof spaced from said path aidjacent one of said barrier walls; and,a second magnetic member supported in said cavity adjacent said pathandspaced from said U-shaped member, said second member having a U-shapedportion with the side arms thereof disposed in overlapping, spacedrelationship to the other of said side arms and embracing said path, andthe base thereof disposed spaced from said path adjacent the other ofsaid barrier walls. I

2. The circuit breaker of claim 1 and in which the U- shaped portionbase of 7 said second magnetic member is supported adjacent the entranceto said passage.

3. The circuit breaker of claim 2 and in which said second magneticmember is in the form of an H,-twoadjacent arms of said H extending inoverlapping relationship to the legs of said U-shaped member, and theadjacent legs of said H extending to said other of the barrier walls anddefining with said other of the walls and the cross-bar of the H anopening adjacent the entrance to said passage.

4. A circuit breaker having a case including opposing barrier iwallsdefining a partially enclosed cavity therein and a passage communicatingbetween said cavity and the outside of said case, switch means disposedin said case including a fixed contact mounted in said cavity and amovable contact in said cavity capable of limited movement betweenopened and closed positions, means mounted in said case and responsiveto overload for opening said switch means, a U-shaped member of magneticmaterial supported in said cavity adjacent the path of movement of saidmovable contact near the opened position thereof, said U-shaped memberbeing disposed with the,

walls, the improvement comprising a substantialiy H- 5 a v 5 shapedmember of magnetic material supported in said and other -0f the walls anopening adjacent the entrance cavity adjacent said path near said fixedcontact, said H- to said passage. shaped member also being disposedadjacent said passage with a pair of adjacent arms thereof embracingsaid path References Cited In the file of 1115 P and the lower armsthereof bearing against the other of 5 I UNITED STATES PATENTS saidbarrier walls, the cross-bar of said H-shaped member L i being spacedbetween said path and said other of the, Hal-a 1940 walls and \definingwith the other pair of adjacent arms l Rypinski et lune 1959

1. A CIRCUIT BREAKER COMPRISING, IN COMBINATION, A CASE HAVING INTERNALOPPOSING BARRIER WALLS DEFINING A PARTIALLY ENCLOSED CAVITY THEREIN ANDHAVING A PASSAGE COMMUNICATING BETWEEN SAID CAVITY AND THE OUTSIDE OFTHE CASE; SWITCH MEANS DISPOSED IN SAID CASE AND INCLUDING A FIXEDCONTACT MOUNTED IN SAID CAVITY AND A MOVABLE CONTACT LOCATED IN SAIDCAVITY AND CAPABLE OF LIMITED MOVEMENT BETWEEN OPENED AND CLOSEDPOSITIONS; MEANS MOUNTED IN SAID CASE AND RESPONSIVE TO OVERLOADCONDITIONS FOR OPENING SAID SWITCH MEANS; A U-SHAPED MAGNETIC MEMBERSUPPORTED IN SAID CAVITY ADJACENT THE PATH OF MOVEMENT OF SAID MOVABLECONTACT WITH THE SIDE ARMS THEREOF EMBRACING SAID PATH AND THE BASETHEREOF SPACED FROM SAID PATH ADJACENT ONE OF SAID BARRIER WALLS; AND, ASECOND MAGNETIC MEMBER SUPPORTED IN SAID CAVITY ADJACENT SAID PATH ANDSPACED FROM SAID U-SHAPED MEMBER, SAID SECOND MEMBER HAVING A U-SHAPEDPORTION WITH THE SIDE ARMS THEREOF DISPOSED IN OVERLAPPING, SPACEDRELATIONSHIP TO THE OTHER OF SAID SIDE ARMS AND EMBRACING SAID PATH, ANDTHE BASE THEREOF DISPOSED SPACED FROM SAID PATH ADJACENT THE OTHER OFSAID BARRIER WALLS.